Now that large parts of the structure of photosystem II and photosystem I have been determined by different research groups, we want to study in detail several physical processes that occur at the molecular level in photosynthetic systems. In particular we want to study the physics behind non-photochemical quenching (NPQ). NPQ is a reversible protection mechanism that is turned on in bright sunlight. It protects the plant against over-excitation and thereby against photo-inhibition by transforming excess excitation energy into heat. Despite a large amount of scientific research worldwide, the process is still poorly understood and it probably consists of many different sub-processes.